Ending Violence: Lessons From Naked Mole-Rat Sperm

BioMed central recently discovered something peculiar about naked mole-rat’s sperm.

The underground hive creatures, who look like sabre-toothed sausages, have some of the worst swimmers in the animal kingdom. How did things get this way? First, a little back story.

The animals, which can run just as fast backward as forward, feel no pain in their skin, are blind, and recognize their colony by the smell of their dung, live in a hive culture. Each colony has a queen who chooses about three males to mate with. The remaining males defend the hive or forage for food.

…the queen…uses physical force to subdue the remaining males…This created a condition in which it never made sense for sperm to compete with each other.

Once the queen has decided which males to mate with, she uses physical force to subdue the remaining males and females. The dejected males give up and forage for food or attempt to mate with other females. The queen keeps mating with her three chosen mates and has babies with all of them.

This created a condition in which it never made sense for sperm to compete with each other. South African scientists analyzed sperm from three different strata of naked mole-rat, and found no difference between them. Only 1 to 15 percent of the sperm could swim, and only 1 percent of those were any good at it.

And yet, while the sperm appeared to have “devolved,” the fathers were actually very fertile.

Reproductive Choice and Nonviolence

As I mentioned in the article about Robert Sapolsky’s lectures, male competition over access to females is the source of most violence in the animal kingdom. The story is no different for humans.

The naked mole-rat is the exception that explains the logic of the rule. Females compete with each other, sometimes to the death, in order for the right to become queen. This gives her the right to choose which males to mate with.

The males, on the other hand, don’t fight with each other. It wouldn’t offer them any reproductive benefit. This has caused them to become cooperative with each other in every way, all the way down to their sperm.

Why Bonobos and Chimps Behave So Differently

Bonobos: Our closest living relative

Another recent study compared the sperm of chimps and their close cousins: bonobos. It discovered that chimp sperm has a diverse gene pool, while bonobo sperm does not. Those who understand the behavior of these two species, as well as some basic evolutionary theory, shouldn’t be surprised by these findings.

Chimps take females by force. They systematically beat all of the females in their group until they submit. When a female ovulates, she may be forcibly taken by several males. Chimp sperm, like sperm in many species, have evolved to compete with other sperm.

Chimps do not commit violence because they are evil. They commit violence because it provides them with a reproductive advantage.

Chimps do not commit violence because they are evil. They commit violence because it provides them with a reproductive advantage. Shockingly, chimps have been known to commit genocide for this very reason.

It’s understandable that this kind of nihilistic logic is scary to people. And yet it is a truth that we can’t afford to ignore. Most violence is committed because it is beneficial for those who commit it.

Yet Bonobos, who are very closely related to chimps, are almost entirely peaceful. Conflicts are resolved not by aggression, but by sexual gestures. Females cooperate in order to suppress any violent attempts by males. This makes aggression between males pointless, all the way down to their sperm.

Unlike the naked mole-rat, the female bonobos have no reason to be aggressive with each other either. Since they rely on one another for protection, aggression does not benefit them.

Human Sexual Choice

Bonobo and naked mole-rat cultures reduce male aggression by giving sexual choice to the female. Something similar happened in the evolution of humanity. Females evolved something called concealed ovulation.

…human females don’t overtly display when they are “in heat.”…In other words, female sexual choice is an important part of what made us human.

Unlike other species, human females don’t overtly display when they are “in heat.” Where ovulating chimps are essentially raped by males routinely, the introduction of concealed ovulation dramatically reduced the reproductive “benefits” of rape.

In other words, female sexual choice is an important part of what made us human.

This change gave rise to the emergence of monogamy as the most common form of reproduction for humans. Monogamy is common in the animal kingdom, but humans are the only group living primates that are also primarily monogamous. It’s no coincidence we’re the only primate species that practices concealed ovulation.

This may explain differences in violence between humans and chimps. While the use of lethal force appears to be the same in chimps as in subsistence human societies, the use of non-lethal violence in chimps is between 100 and 1000 times higher or more.

Ending Violence

Except in pathological cases, the majority of violence is committed for personal gain. These lessons from the animal kingdom provide us with the key to ending violence. Take away the benefits it provides.

And this is why, despite its visibility in the media, violence is becoming increasingly rare among humans, as Steven Pinker has pointed out. Slavery, genocide, colonialism, and torture were once proudly proclaimed tenants of society. It was widely accepted that people could be murdered for committing misdemeanors, believing the wrong things, or for entertainment.

…[if] the twentieth century saw the same levels of violence as those observed in tribal societies…the wars of the past century would have killed two billion people.

To get an idea of just how much violence has declined, suppose that the twentieth century saw the same levels of violence as those observed in tribal societies. Rather than killing 100 million people, the wars of the past century would have killed two billion people.

By holding people accountable for their crimes, government has reduced homicide. Early governments were much like female naked mole-rats, using violence to eliminate the benefits of violence for everybody else.

But by holding government accountable for its actions, democracy has reduced warfare between governments as well.

Furthermore, by allowing both parties to benefit instead of just one, commerce has replaced genocide as the primary method of acquiring real estate.

In the 1950s, 65,000 people died per year from warfare. During the 2000s, the figure was as low as 2,000 deaths.

The past century also saw a dramatic drop in violence. In the 1950s, 65,000 people died per year from warfare. During the 2000s, the figure was as low as 2,000 deaths.

I’m not implying that these changes are the result of biological evolution, which isn’t fast enough to cause these changes. Besides, eighty percent of people admit to fantasizing about killing somebody they don’t like.

Thankfully, the fact that humans have the foresight to predict how their behavior will affect their future has provided us with a shortcut. Cultural changes that eliminated the benefits of violence have reduced its prevalence. The resulting lack of threats has allowed us to exercise empathy outside the context of our immediate social group.

Take away the benefits of violence, and it won’t be committed. Perhaps one day we’ll see our violent instincts atrophy just like the naked mole-rat’s sperm. Until then, we’ll need to keep searching for new cultural solutions.

If you’ve got a suggestion, I’d like to hear it in the comments.

Trade-offs: Sometimes You Can’t Be Harder, Better, Faster, and Stronger

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  • http://none private

    Instead of wasting a lot of time being specific about why I disagree with your article, especially the part which deals with the end of violence I hope you don’t mind if I post a review of pinkers book. http://douthat.blogs.nytimes.com/2011/10/17/steven-pinkers-history-of-violence/
    Also, I don’t know where you live but in the United States the rate of violent crimes is rising. Feel free to check the statistics. Here is a link. http://www.disastercenter.com/crime/uscrime.htm